export-mobile

name	export-mobile
description	Re-encodes an existing py5 artwork's MP4 to mobile-optimized format: H.264/10–20s seamless loop, two orientations (landscape 1280×720 and portrait 720×1280). Takes a work name as argument. Triggers: export mobile, mobile export, mobile video, re-encode for mobile
allowed-tools	Bash, Read, Write, Edit

Export Mobile Skill

Re-encode an existing artwork's video as mobile-optimized MP4s — one landscape and one portrait.
No new sketch is created — only the existing rendered video is transcoded.

Output Spec

Item	Landscape	Portrait
Container	MP4	MP4
Codec	H.264 (libx264, baseline, level 3.1)	H.264 (libx264, baseline, level 3.1)
Resolution	1280×720	720×1280
Duration	10–20 seconds (see duration rules below)	10–20 seconds (same TARGET_SEC)
Loop	Seamless — uses -stream_loop -1 + -t	Seamless — uses -stream_loop -1 + -t
Fast-start	-movflags +faststart	-movflags +faststart
Quality	-crf 23	-crf 23
Scaling	Fill + center-crop (no black bars)	Fill + center-crop (no black bars)
Output file	{work_name}_landscape.mp4	{work_name}_portrait.mp4

Inputs

• Work name: passed as the argument to the command (e.g. lbm_karman_vortex_street)
• Source file: sketch/{work_name}/{work_name}.mp4

Workflow

1. Receive the work name from the command argument.
2. Verify sketch/{work_name}/ exists. If not, stop and report the error.
3. Find the source MP4. Try in this order: a. sketch/{work_name}/{work_name}.mp4 b. Any single *.mp4 file in sketch/{work_name}/ that does not end with _landscape.mp4 or _portrait.mp4 If no source found, stop and report.
4. Get the source duration:

   ffprobe -v quiet -show_entries format=duration -of csv=p=0 sketch/{work_name}/{work_name}.mp4
   

5. Determine TARGET_SEC using these rules (applies to both outputs):
   • Source is 10–20 s → use source duration as-is (no loop, no trim)
   • Source < 10 s → TARGET_SEC = 15 (loop to fill)
   • Source > 20 s → TARGET_SEC = 15 (trim to a centered segment)
6. Run FFmpeg for landscape (1280×720):

   ffmpeg -y -stream_loop -1 \
     -i sketch/{work_name}/{work_name}.mp4 \
     -t {TARGET_SEC} \
     -vcodec libx264 \
     -profile:v baseline -level 3.1 \
     -vf "scale=1280:720:force_original_aspect_ratio=increase,crop=1280:720" \
     -pix_fmt yuv420p \
     -movflags +faststart \
     -crf 23 \
     sketch/{work_name}/{work_name}_landscape.mp4
   

7. Run FFmpeg for portrait (720×1280):

   ffmpeg -y -stream_loop -1 \
     -i sketch/{work_name}/{work_name}.mp4 \
     -t {TARGET_SEC} \
     -vcodec libx264 \
     -profile:v baseline -level 3.1 \
     -vf "scale=720:1280:force_original_aspect_ratio=increase,crop=720:1280" \
     -pix_fmt yuv420p \
     -movflags +faststart \
     -crf 23 \
     sketch/{work_name}/{work_name}_portrait.mp4
   

   -stream_loop -1 with -t handles both looping (short source) and trimming (long source).
   force_original_aspect_ratio=increase + crop fills the entire target frame from the center, avoiding the small-video-with-black-bars problem that occurs with decrease + pad.
8. Verify both output files were created successfully.
9. Report: work name, source duration, target duration, and for each output — path and file size.

Notes

• Output filenames follow the pattern {work_name}_{orientation}.mp4 (landscape or portrait).
• Never overwrite the original source file.
• Do not modify main.py, WORKS.md, or FEEDBACK.md.
• Do not commit unless explicitly requested.
• If the source video does not exist at all (artwork never rendered), report clearly: "Source MP4 not found. Run the sketch first to generate {work_name}.mp4."